In oilfield operations, drilling process may be impeded by a wide variety of problems. An accurate measurement of downhole conditions, rock properties and surface equipment enables many drilling risks to be minimized and thereby improves operational efficiency of the drill rig.
It is observed that for efficient drilling of oil and gas wells, it is essential to generate reliable and accurate real-time operation monitoring data at the rig-site. The cost reduction in drilling of oil and gas wells and improvement of operational efficiency of the drill rig is achieved by reducing non-productive time.
Conventionally non-productive time of the drill rig is monitored and controlled by measuring real time variables e.g. bit depth, bore hole depth, true vertical depth and bit on bottom status. Reliable and precise measurement of real time variables enables better quantification and measurement of drilling performance. The existing technologies also describe a method of automated drilling performance analysis from real time data. Since bit depth, bore hole depth, true vertical depth and bit on bottom status determination depend on slip status value of the drill string, reliable and precise determination of slip status enables minimizing non-productive time and maximizing drilling performance and hence drilling operational efficiency.
Further, operational efficiency may also be improved by faster footage drilling per hour. The drilling performance key performance indicators (KPI) are derived from drilling operational data and help in drilling operational efficiency measurements and improvements. Tripping rate KPI is determined from bit depth and stand counter change rates while running in and pulling out of drill pipes. Casing run rate KPI is also determined from bit depth and stand counter change rates while running in casing joints. Bit Depth and Stand Counter change are determined from Slip Status as a primary parameter. Hence, accurate measurement and better control of tripping rate largely depends on reliable and precise values of slip status of the drill string. Therefore, it may be understood that drilling operational efficiency depends on reliable and precise values of slip status.
Some of the conventional technologies also suggest drilling operational efficiency improvement by effective collaboration between Rig-system and real time operational centre system (RTOC). Reliable and precise values of slip status enable good quality drilling operational data. This data is transmitted in real time from rig system to town based RTOC system where experienced engineers provide critical real time remote decision support to drilling operations. RTOC system also supports workflows and applications which can predict drilling hazards prior to happening of event and suggest timely mitigation methods to rig team. Therefore, it can be concluded that reliable and precise slip status values enable effective collaboration and improved drilling operational efficiency.
In light of the above it may be understood that improvements in operational efficiency of the drill rig can be achieved by reliable and accurate measurement of slip status. Generally, determination of slip status (SST) depends on quality of available real-time hook load (RTHL) data and the hook load threshold (Pre-configured value of Threshold HL-PCTHL). The conventional method which is widely followed for determination of SST is based on PCTHL. In such conventional methods of SST determination, PCTHL is static, manual and based on individual judgement. This approach is usually error prone and likely to lead to incorrect PCTHL specification that result in unreliable and inaccurate SST determination. Also, in practical drilling operation, the PCTHL value may need to be specified according to the changing values of hook load, hook speed and hook movement etc. This mechanism fails to provide accurate determination of SST at the beginning, end of trip and at beginning of casing run job when string weight is low. This leads to inaccurate determination of bit depth and stand counter values at beginning of and end of trips and beginning of casing job. In the absence of automated accurate slip status measurement mechanism at beginning and end of trips, real time drilling operational data e.g. bore hole depth, bit depth, true vertical depth, bit on bottom and stand counter cannot be determined accurately, adversely affecting operations monitoring and drilling operational efficiency measurement and improvement.
In light of the foregoing discussion, there is a need to develop an improved method for determining accurate slip status of the drill string to overcome one or more limitations stated above.